Searching for Monoenergetic Neutrinos Arising - PowerPoint Presentation

Slide1

Searching for Monoenergetic Neutrinos Arising From Dark Matter Annihilation

Jason Kumar

University of

H

a

w

a

i

iSlide2

collaborators

Jin In

Carsten

Rott

Pearl Sandick

Jennifer Gaskins

David Yaylali

1502. 02091, 15xx.xxxxxSlide3

dark matter and monoenergetic neutrinossearches for dark matter using

neutrino detectors

dark matter collects in the

core of the sun

after

scattering

off solar nuclei

annihilates

to Standard Model products, and the

neutrinos

get out

reach

neutrino detector

on earth

focus is typically on a

smooth

distribution of events above background

why?

often assumed

no direct annihilation to neutrinos

neutrinos arise from decay of other SM states

mostly have studied detection strategies in which

neutrino energy can’t be fully reconstructed

anyway

see a smooth distribution of charged leptons

I’ll focus on a different possibility

models in which dark matter can produce

monoenergetic neutrinos

detectors and strategies which can

resolve a line signalSlide4

basic pointsexperiment

electron neutrinos

undergoing charged-current interaction will

deposit almost all energy in the detector

some neutrino detectors, like

liquid scintillation

detectors or

liquid argon TPCs

, can

reconstruct energy

and

direction

of incoming neutrino

can determine if neutrino emanates from the

sun

sensitive to a

line signal

theory

in the absence of

minimal flavor violation

, or with

non-Majorana dark matter

, can easily have dark matter annihilate to

monoenergetic neutrinos

dark matter models which annihilate to u, d, s quarks produce plenty of

π

+

,

K

+

stop before they decay

(producing more

π

+

)

produce

monoenergetic neutrino Slide5

neutrinos from the sunbasic ideaDM scatters off solar nuclei, loses energy through

elastic scattering

falls below

v

esc



captured

orbits, eventually collects in coreDM annihilates to SM matterSM decay yields neutrinos  seen at detectorDM in equilibrium  GC = 2GAso neutrino event rate probes DM capture rate (∝ sSI ,sSD)usually look for hard neutrinoslight hadrons stop before decaying  soft neutrinos

Dawn Williams

A.

Zentner

, arXiv:0907.3448Slide6

why (not) χχν̅ν?

can understand just from

angular momentum

for Majorana fermion, wavefunction is

anti-symmetric

L=0

,

S=0

or L=1, S=1if outgoing fermions on z-axisLz=0 ( Ylm(q=0,f)≠0 only if m=0 )Sz = Jzif Sz=0 need f, f̄ with

same helicitynot CP-conjugateneed

Weyl spinor mixing

in MFV, mixing scales with mass

if

S

z=±1 need f, f̄ with opp. helicityno mixing needed

J=0, L

Z

=0

 S

Z=0

J

z

=1, LZ=0  SZ=1

f

L

f

R

f̅R

f

̅

RSlide7

monoenergetic neutrinosthis argument underlies the theoretical prejudice

towards searches for the b

̅

b,

τ̅

τ

and W

+

W- channels but the chirality suppression arises from the assumption of Majorana fermion dark matter and minimal flavor violationcertainly true for the CMSSM, but need not be true in generalWIMPs need not be Majorana, and MFV can fail even in the general MSSMif dark matter is a Dirac fermion, then the initial state can be L=0, S=1, J=1, so s-wave annihilation, but no mixing neededif we drop minimal flavor violation, then mixing need not scale with masseither way, χχν̅ν branching fraction could be O(1)or χχ q̅q

for q = u, d, s worth studying these annihilation channelsSlide8

why not light hadrons?usually ignore

χχ



q

̅

q

for q=

u,d,s

why?  another reason....u, d, s  light hadrons which stop in the sun before decaycare about pions, kaonsresulting ν spectrum is very softlarge background, small detector effective areabut the stopping process produces a large number of pions

trade a hard spectrum for a softer one, but with

larger fluxBeacom,

Rott, Siegal-Gaskins (1208.0827)

π

+

π

-

π

0

K

+

q

̅

qSlide9

spectrum care about π

+

and

K

+

π

0



γγ π- Coulomb-captured by nuclei, and absorbeddoesn’t produce a lot of neutrinosmain relevant decay is π+, K+  νμ μ+ monoenergetic neutrino with E = 29.8

MeV (pion) or

235.5 MeV

(kaon)

oscillates into

monoenergetic

νe , and can produce a line signalmuon stops in sun before decay

μ+  e+

νe

ν̅μ also get continuum ν

e, ν̅μ from

μ+ decay, but less distinctivejust need the fraction of DM energy which goes into stopped

π+, K

+r ≡

fraction of center-of-mass energy which goes into π+, K+ determine r in Pythia/GEANT

rπ ~ 0.1 Slide10

resolving a line signalessentially need two things

full energy

containment

directionality of charged lepton

track (for high energy)

need

ν

e

charged current interaction produces e± produces short-range cascade which is fully-contained in detectorat high Eν, muon is long-rangereduces the effective volumeat Eν = 30 MeV, can’t produce muon

ν



θ



f

≡

fraction of events in θcone f

ν ~ 0.4fν̅ ~

0.8reduces bgd at large Eν but at Eν≈30

MeV, no direction Slide11

LS detectorscintillator produces a spherical burst of light

essentially a

calorimeter

easy

to get

total energy

harder

to get

direction

from a spherical burst of lightbut timing of when PMTs are illuminated can be used to reconstruct charged lepton trackessentially, Huygen’s principleanalysis of KamLAND data is on the way....we’ll treat it as our benchmark detector ....figures courtesy of John LearnedSlide12

what we need....we have the neutrino fluxes from the sun arising from DM

....

we have

estimates of the

ν

e

background

at E > GeV (for

χχν̅ν)at E ~ 30-300 MeV (for meson decay)charged current neutrino-nucleus scattering cross sectionfor E > GeV, get σ  E (DIS)for E ~ 30-300 MeV, more complicatedcross sections smaller at low EνHonda

Battistoni, Ferrari, Montaruli, SalaSlide13

sensitivity at high energybenchmark = KamLAND

V = 500 m

3

T = 3600 days

ε

~

few % (5 %)

beats current DD limits

no big suppression at low mass, unlike direct detectionSuper-K winslarger exposure due to sizeSK has larger bgd., but KamLAND is signal limitedcan’t fully benefit from low background yet LBNE DUNE?  ε ~ 3 %, 10× exp.flavor-indep, 90% CLSlide14

sensitivity for charged meson decayat low energy, take

ε

~

1 %

for

LS

KamLAND is

signal limited

viable models produce < 1 event in

KamLANDs exposureproblem  σνA small at low Eν DUNE could do much better (34 kT LAr TPC, 1 year)

still negligible background

1 year, ε

~ 10 %

competitive with direct detection

at

~ 5 GeV other neutrino searches not sensitive (focused on high-energy neutrinos)

90% CLSlide15

signal limitedlook at π

+

decay, 10 GeV,

LArTPC

if

ε

≲

0.1, would need ~ 10 years to get a single bgd. event in a binS/B doesn’t depend on exposure or target, just on fluxes and energy resolutionif S = B, then σSDp ≈ 0.07 pb ⨯ ε Ecrit exposure needed to get a single signal event at S = B (= 1)

exposure = (M/kT) (T/yr)

to fully realize potential at 5% energy resolution, need

625 kT yr

LArTPC

detectorLS  factor 8× largerSlide16

signal limitedconsider monoenergetic neutrino signal at m = 10 GeV

again at

LArTPC

,

ε

~

5%

compare to analysis of

monoenergetic neutrinos from π+ decaybackground neutrino rate is about ~ 4900 smaller signal neutrino rate about ~ 13 times smaller (fixed σSDp)no enhancement arising from multiple pionseffective area ~ 104 ⨯ largerenergy dependence of scattering cross section

at S/B = 1 limit, would have σSD

p

≈ 10-5

pb

need a

~ 270 kT yr detector exposure to get ~ 1 signal eventχχ

ν̅ν channel has better sensitivity, smaller exposure, ... if it’s there

but to fully exploit either strategy, one would need an exposure similar to a

34 kT DUNE running for 10 – 20 yearsSlide17

dark matter annihilation in the sun can produce

monoenergetic

neutrinos

need non-Majorana, or non-MFV, for direct annihilation

to neutrinos

or decays of numerous stopped

π

+

LS or LArTPC neutrino detectors can reconstruct energy and directionneed electron neutrinos for fully-contained shower

reduced backgrounds

but current detectors are signal-limited, so need bigger detectors and larger run-times

.... (DUNE?

THEIA?)

c

onclusion

M

a

halo

!Slide18

Back-up slides